It is well known that styrenic homopolymers and copolymers of styrenic compounds and acrylonitrile have poor impact strength. In order to improve this impact strength, rubber is added to these resins where it acts as a reinforcing agent. A widely used method comprises polymerizing a styrenic compound and an unsaturated nitrile in the presence of an unsaturated rubber. The obtained products are more stable and have superior properties when compared with similar products prepared by other methods, such as blending or milling.
One usual technique for preparing rubber reinforced styrenic resins by grafting chains of homo- or copolymers of a styrenic compound onto a rubber consists of carrying out the polymerization either by an all emulsion process or an all suspension process or a mass-suspension process. Such techniques present an economic problem, as the manufacture of these reinforced styrenic resins depends on rubber supplies.
In order to decrease the costs of the resins and to obviate some drawbacks of the prior processes, it has been proposed to prepare rubber reinforced styrenic resins by forming the rubber particles in situ in the presence of a rigid styrenic resin. The process comprises contacting a polystyrenic matrix and a monomer or a mixture of monomers forming a rubbery polymer or copolymer by polymerization and then suspension polymerizing said monomer(s) with formation of a rubber partly grafted to the matrix. The production of rubber reinforced synthetic resins by this method is a batch-process. Moreover, the beads of the final resin must be washed, centrifuged and dried.
There exists a need in the art, therefore, for a less expensive method for producing rubber reinforced synthetic resins.